It is important to identify precisely the nature of certain types of small particles. For example, various biologically active species such as different types of viruses have widely varying effects on living organisms. Some may have little effect, and others may be deadly. Persons who are potentially exposed to viruses need an accurate approach to rapidly and accurately identify the nature of such viruses, so that preventative measures or countermeasures may be employed as necessary. In other cases no action need be taken with viruses that are not potentially injurious.
A number of chemical and physical techniques are useful for identifying small particles such as viruses. Chemically active small particles may be analyzed by observing their chemical reactivity. In one technique, the particles are captured in a filter and then chemically tested by determining their reactivity with other species or with particular chemicals. Such chemical testing may be quite slow in providing an identification, however. Small particles may also be analyzed according to physical properties, such as by X-ray diffraction to determine their internal structure. This approach also requires a considerable time and also cannot be performed readily on small numbers of very small particles. Small particles may also be captured and visually analyzed to estimate their masses, using a powerful microscope such as a scanning electron microscope. This technique does not yield information in real time, and it requires the availability of a scanning electron microscope.
In another approach which is used to analyze larger particles and has the potential for real-time analysis, a light beam is passed through an entrained flow of the particles. The scattered light beam is used to obtain a distribution of sizes of the particles, which may be approximately related to a distribution of particle masses. However, light scattering is not useful to detect particles which are much smaller than the wavelength of light, as is the case for viral particles.
There is therefore a need for an approach to rapidly and accurately analyzing for the presence and nature of small particles in the atmosphere and elsewhere. The present invention fulfills this need, and further provides related advantages.